This invention relates to a method of producing blister copper pyrometallurgically in a suspension reactor directly from Its sulfidic concentrate. According to the method a copper sulfide concentrate is fed into a suspension reactor, into which cooled and finely ground copper matte is also fed in order to bind the heat released from the concentrate.
A well-known method of the prior art is to produce raw copper or blister copper from a sulfidic concentrate in several stages, whereby the concentrate is smelted in a suspension reactor, such as a flash-smelting furnace, with air or oxygen-enriched air, which results in copper-rich matte (50-75% Cu) and slag. This kind of method is described in e.g. U.S. Pat. No. 2,506,557. Copper matte formed in a flash-smelting furnace is converted in for example a Peirce-Smith type converter or flash converter into blister copper and refined further in an anode furnace.
The production of blister copper from sulfidic concentrate directly in one process step in a suspension reactor is economically viable within certain boundary conditions. The greatest problems involved in the direct production of blister include copper slagging to slag, the large amount of slag formed and the large amount of heat released on burning the concentrate. The large amount of slag requires a large smelting unit in surface area, which affects the investment costs of the process.
Besides the amount of slag, one problem arising in the direct production of copper is the large amount of heat formed in the burning of sulfidic concentrates, due to which the oxygen enrichment when burning normal concentrates (copper content 20-31% Cu) must be low, even under 50% oxygen, whereby the heating of the nitrogen in the process air balances the heat economy. This, however, results in a large amount of process gas, which in turn entails a large furnace volume and above all to large gas treatment units (boiler, electric precipitator, gas line, acid plant washing units etc.) In order to make these units related to gas handling a more economical size, the aim should be to get a high oxygen enrichment in the suspension reactor (over 50% O2 in the process gas).
If the copper content of the concentrate is high enough, typically at least 37% Cu, as for example at the Olympic Dam smelter in Australia, where the copper content of the concentrate exceeds 50%, it is possible to produce blister directly in one stage, since the thermal value of the concentrate is usually lower the higher the copper content of the concentrate. In fact, at high copper content the proportion of iron sulfide minerals is low. When using the previously described concentrate, high enough oxygen enrichment can be used and, as a result the amounts of gas remain moderate.
Concentrate with a lower copper content can also be suitable for direct blister production, if it has an advantageous composition. For example, at the Glogow smelter in Poland, blister copper is produced from concentrate in one stage, since the iron content is low and the resulting amount of slag is not significantly high. The production of copper in one stage with normal concentrates causes slagging of all the iron and other gangues. This type of method is described in U.S. Pat. No. 4,030,915.
Now a new method has been developed to produce blister copper in a suspension reactor, in which method cooled and finely ground copper matte is fed into the suspension reactor with a concentrate in order to bind the heat released by the copper sulfide-containing concentrate and to reduce relatively the amount of slag. Copper matte is produced in a separate unit, cooled for example by granulating and then ground finely. By the term relative reduction in the amount of slag it is meant that a smaller amount of slag is generated with regard to the amount of blister copper produced than by the conventional method. By means of this method it is possible to use high oxygen enrichment in direct blister production and manage with smaller gas treatment units than earlier. In addition the total smelter capacity can be increased significantly without adding to the total amount of suspension reactor feed. The essential features of the invention will become apparent in the attached claims.
The basic concept behind the present method is that instead of the conventional method, where the additional heat is bound to the nitrogen in the gas, in this method the heat is bound to cooled matte. By adding cooled matte to the concentrate, the oxygen enrichment can be raised as the proportion of matte grow""s both with poor and rich copper concentrates. If the proportion of cooled and finely ground matte in the feed is very great, the oxygen enrichment can be raised significantly even with poor concentrates and direct blister production made economically viable.
Another benefit of the method in the present invention is that the relative amount of slag generated in the suspension reactor decreases as the proportion of matte increases in the feed, whereby copper losses into slag decrease and the amount of copper circulated via slag cleaning also decreases. Iron silicate slag or calcium ferrite slag can be used in a blister furnace depending on the composition of the concentrate. If both matte and blister production take place in the same smelter so that the slag processing can be handled jointly, it is advantageous that both reactors use the same type of slag. If slag concentration is part of the slag processing then it is advantageous that the slag is iron silicate slag. The matte fed into the blister furnace may be matte produced in any kind of known smelting furnace.
A single suspension smelting unit may be designed directly as a blister smelter depending on the copper content and composition of the available concentrates and on the amount and composition of the available matte. The slags are treated further in single-stage or preferably two-stage slag cleaning. The two-stage cleaning method includes either two electric furnaces or an electric furnace and a slag concentrating plant. If the slags are treated in a slag concentrating plant, the slag concentrate can be fed back into the suspension reactor. Blister copper goes for normal refining in an anode furnace.
If two smelting units are available, at least one of which being a suspension smelting furnace, normal copper concentrates are handled in the matte producing unit. The matte produced is granulated and fed, finely ground, int the blister smelting unit together with the concentrate, whereby blister furnace concentrate is richer than normal (Cu content over 31%). Slag from a matte producing furnace is treated according to the prior art, for example, in a slag concentrating plant, and blister furnace slag is treated advantageously first in an electric furnace, from where the slag goes to the slag concentrating plant In this case too, blister furnace slag treatment can be single-stage.